1. The Field of the Invention
The present invention is related to methods and apparatus for spreading rock dust in mine tunnels in order to prevent fires and explosions. More particularly, the present invention is related to methods and apparatus for rock dusting mine tunnels, which apparatus is self-propelled and is capable of traveling along the top of a conventional mine conveyor system.
2. The Background of the Invention
It is well known that fires and explosions are a major hazard in the field of underground mining. The danger of fire and explosion is particularly acute in coal mining because of the existence of inherently explosive and flammable materials, such as methane gas and coal dust, in the underground coal mine. The history of underground coal mining in the United States and in other countries of the world has been punctuated by frequent fires and explosions. Associated with such fires and explosions is the almost certain loss of life and personal injury which flows from such occurrences. For example, it is estimated that from 1980 through 1984, over 53,000 miners were injured and over 450 miners lost their lives in coal mine accidents, many as a result of fire or explosion. See Statistic Abstract of the United States at 680 (1987).
The cause of such fires and explosions can be readily appreciated. Combustible materials are generally associated with the mining of materials, such as coal, which are based on organic chemicals. Not only is the coal itself is combustible, but the mining operation produces small fragments of coal and coal dust which is introduced into the air. This material may well be combustible and even explosive under appropriate conditions.
As mentioned above, it is also well known that hydrocarbon gases are found in association with coal mine operations. The most commonly found gas is methane gas, the major component of natural gas. Other similar combustible hydrocarbon gases are also found in lesser quantities in association with coal mines. It will be appreciated, therefore, that the gaseous materials which are released during coal mine operations are themselves extremely hazardous.
It will also be appreciated that coal mine operations can often result in sufficient sparks to ignite combustible and explosive materials. Coal mine operations require the use of many types of electrical apparatus as well as other types of machinery which can potentially produce sparks. The combination of spark-producing machinery and electrical equipment, and the extremely explosive and combustible coal dust and related gases, produces a hazardous situation.
the combination of potentially spark producing equipment and extremely combustible material found within underground mines has resulted in disaster on many occasions. In addition, underground explosions and fires are particularly difficult to survive. For example, the explosion may cause collapse of part of the mine tunnel. Fire and explosion underground produces large quantities of noxious gases which can easily produce personal injury or death to underground miners and others working underground. Thus, it can be seen that fires and explosions in underground mine operations are of particular concern to all involved.
Various solutions have been attempted in order to prevent fire and explosion in underground mine operations. One traditional method of minimizing the potential for fire and explosion has been to spread inert material within the interior of the mine. In some cases it is desirable to totally coat the interior walls, ceiling and floor of the mine tunnels. Adding inert material to the environment helps to maintain the ambient atmosphere within the mine at conditions which are not explosive or combustible. The inert materials spread onto the interior walls of the mine sufficiently dilutes the mine dust and methane within the mine such that the atmosphere is not capable of propagating an explosion or fire. The coating also helps prevent further coal dust and the like from escaping into the air within the mine tunnel.
This method of preventing explosions and fires within the mine has become accepted in the art. Indeed, under regulations promulgated pursuant to the Federal Coal Mine Health and Safety Act, dusting is now a requirement in many mines.
Regulations of the Mine Safety and Health Administration ("MSHA") provide that the interior of coal mines and the like should be coated with a coating of "rock dust." Rock dust is defined by MSHA as pulverized limestone, dolomite, gypsum, anhydrite, shale, adobe, or other inert material, preferably light colored, 100 percentum of which will pass through a sieve having 20 meshes per linear inch and 70 percentum or more of which will pass through a sieve having 200 meshes per linear inch. See 30 C.F.R. .sctn.29.4 (1986).
MSHA also sets forth regulations concerning the use and spreading of "rock dust." These regulations require the use of rock dust in many situations. In particular, those regulations state that:
All underground areas of a coal mine, except those areas in which the dust is too wet or too high in incombustible content to propagate an explosion, shall be rock dusted to within 40 feet of all working faces, unless such areas are inaccessible or unsafe to enter or unless the Secretary or his authorized representative permits an exception upon his finding that such exception will not pose a hazard to the miners. All crosscuts that are less than 40 feet from a working face shall also be rock dusted. 30 C.F.R. .sctn.75.402 (1986).
Obviously, extensive governmental regulations governing the use and administration of rock dust are now in place. Furthermore, the situations in which rock dust is required are also defined in detail by specific regulation. Thus, it can be seen that mine operators now find themselves in the position of being required to comply with extensive regulation regarding rock dusting. Rock dusting within coal mines, therefore, is often no longer just one alternative to dealing with potentially hazardous conditions, but rather, is absolutely required in many settings.
As a result of the safety hazards presented by explosive materials in a mine, as well as the requirements of federal statute and regulation, methods and apparatus for rock dusting are of prime importance in coal mine operations. Various methods and devices have been developed to allow the spread of rock dust.
One of the early methods of rock dusting coal mine operations was simply to provide a powerful blower at the entrance of a tunnel. The blower would blow shale rock or similar substances into the mine. The problem with this method, however, was that a great many places within the mine remained unprotected from coal dust explosions. The single fan at the entrance of the tunnel could not provide sufficient thrust to drive rock dust into every corner of the mine. In addition, this method was found to be very uneconomical because of the large size and expense of the machinery necessary, as well as the labor cost in operating the machine and in feeding coal dust into the machine. In addition, it was generally necessary to close the mine to allow for the application of rock dust.
An improvement on the method of simply blowing dust into a mine, was to introduce that dust in liquid form. Using this method, the powdered shale, clay, adobe, or other similar inert material was mixed with water in a large tank to form a thick fluid or paste. This fluid or paste was them pumped through a centrifugal pump and was sprayed onto the walls of the mine tunnel. In liquid form, the dust was able to penetrate many areas which were missed by simply blowing dust into the mine.
This method, however, suffered from several drawbacks. First it was necessary to provide a large source of water at the mine. Depending on the location of the mine, this could be extremely difficult. Also, compared with dry rock dust, the wet paste is heavy and difficult to handle. Thus, this method was also found to be expensive and difficult to implement.
In order to provide some mobility in using rock dusting methods, it was often desirable to provide a truck frame and wheels on which to mount the sprayer apparatus. In some cases, the truck was provided with railroad-type wheels such that the apparatus could be moved about on the tracks which otherwise accommodated mine cars within the mine. This provided some additional mobility and flexibility, yet many of the problems described above still remained. The dusting operations remained difficult and expensive. In addition, limitations inherent in carrying a supply of rock dust are encountered. For example, frequent reloading of the hopper is required.
Another device of this general type employed a hopper of dry dust set on top of a truck having railroad type wheels. The apparatus included a screw conveyor which unloaded the hopper into the actual sprayer device. The dust was then pumped into a fan, or other type of pumping device from which it was sprayed onto the mine walls. This device, while an improvement over some of the early devices, still suffered from several limitations. For example, the size and weight of the hopper limited the flexibility of the device. Overloading the hopper required the movement of heavy loads of rock dust. If the hopper is too small or insufficiently loaded, however, the hopper must be frequently refilled.
Various adaptations of this general concept have been made. Essentially, a trough or holding container is provided to hold a supply of mine dust. A feed mechanism is then placed in communication with the trough such that the rock dust can be moved out of the trough. The feeding mechanism then feeds the rock dust into a blower mechanism, which in turn allows the rock dust to be manually blown onto the various walls, ceilings, and floors of the mine. Often the wheels are of a type such that they are adapted to fit on the rails which run within the interior of the mine. This provides a certain measure of mobility which otherwise would not be available to a machine of the weight and size of conventional rock dusters. However, the limitations described above remain.
Other modifications to this type of machinery have been made. For example, the exact configuration of the fan mechanism has been varied somewhat. One such rock duster employs a centrifugal broadcasting member whereby dust is discharged from the apparatus and sprayed onto the interior of the mine. Additional fans and other feeding apparatus have been provided in order to prevent the rock dust from packing within the trough. In each of these variations, however, the same basic concept is applied. The apparatus comprises a hopper of limited size, which may be mounted on a mobile truck body. The contents of the hopper are then fed into a sprayer mechanism for discharge into the interior of the mine.
It is clear that one of the major problems in this type of apparatus is the transportation of rock dust within the mine. Each of these mobile sources suffer from the problem of requiring that the apparatus itself transport a supply of rock dust. Once the supply of rock dust is depleted the device must again return to the outside of the mine, or other location, where an additional supply of rock dust can be found.
In order to partially solve this problem, it has been suggested that a conveyor system be used to convey rock dust to the mobile apparatus. Thus, an apparatus having a trough or storage bin and a blower mechanism has been devised. In order to fill the trough, however, it has been suggested that the conveyor belt within the mine be used to deliver rock dust to a more convenient location in order to load the hopper on the apparatus.
While this partially solves the problem, the same basic problem exists as with the other mobile apparatus. IT is still necessary to constantly fill the trough or storage bin during use. The conveyor belt simply provides a more conveniently located stock pile of rock dust. It is still necessary to return to the source of rock dust, (such as the end of the conveyor belt) in order to fill the apparatus. Alternatively, if the bin were to be placed in communication with the end of the conveyor, the apparatus would have extremely limited mobility and usefulness.
It is apparent that what is currently needed in the art are methods and apparatus for easily and effectively applying rock dust within underground mines, such that complete coverage of mine floors, ceilings, and walls is provided. It would also be an advancement in the art to provide such an apparatus where no heavy and bulky hopper was required and, as a result, frequent reloading would not be needed. It would also be an advancement in the art to provide methods and apparatus for applying rock dust which wee mobile and which used independent means of propulsion. It would also be an advancement in the art to provide methods and apparatus for applying rock dust which were not bulky and complex, as are conventional rock dust applicators. It would also be an advancement in the art to provide methods and apparatus for applying rock dust which were economical to use and which did not require closing the mine for extended periods of time.
Such methods and apparatus are disclosed and claimed below.